EP1271199A1 - Optische Einrichtung zur Kompensation der chromatischen Dispersion - Google Patents

Optische Einrichtung zur Kompensation der chromatischen Dispersion Download PDF

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Publication number
EP1271199A1
EP1271199A1 EP01830435A EP01830435A EP1271199A1 EP 1271199 A1 EP1271199 A1 EP 1271199A1 EP 01830435 A EP01830435 A EP 01830435A EP 01830435 A EP01830435 A EP 01830435A EP 1271199 A1 EP1271199 A1 EP 1271199A1
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EP
European Patent Office
Prior art keywords
grating
substrate
optical device
chromatic dispersion
wavelength
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP01830435A
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English (en)
French (fr)
Inventor
Guido Oliveti
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Corning OTI SRL
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Corning OTI SRL
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Publication date
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Priority to EP01830435A priority Critical patent/EP1271199A1/de
Priority to US10/184,711 priority patent/US6760519B2/en
Publication of EP1271199A1 publication Critical patent/EP1271199A1/de
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
    • G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
    • G02B6/02195—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for tuning the grating
    • G02B6/022—Refractive index modulation gratings, e.g. Bragg gratings characterised by means for tuning the grating using mechanical stress, e.g. tuning by compression or elongation, special geometrical shapes such as "dog-bone" or taper
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
    • G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings
    • G02B6/0208—Refractive index modulation gratings, e.g. Bragg gratings characterised by their structure, wavelength response
    • G02B6/02085—Refractive index modulation gratings, e.g. Bragg gratings characterised by their structure, wavelength response characterised by the grating profile, e.g. chirped, apodised, tilted, helical
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
    • G02B6/29305—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide
    • G02B6/29313—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide characterised by means for controlling the position or direction of light incident to or leaving the diffractive element, e.g. for varying the wavelength response
    • G02B6/29314—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide characterised by means for controlling the position or direction of light incident to or leaving the diffractive element, e.g. for varying the wavelength response by moving or modifying the diffractive element, e.g. deforming
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
    • G02B6/29392—Controlling dispersion
    • G02B6/29394—Compensating wavelength dispersion

Definitions

  • the present invention relates to an optical device for compensating chromatic dispersion in optical telecommunications systems.
  • optical fibres used for transmitting signals in optical telecommunications systems show a phenomenon called chromatic dispersion, due to the combination of the characteristics of the constituent material of these fibres and the characteristics of their refractive index profile; this chromatic dispersion is variable with the wavelength of the signals transmitted and is cancelled at a certain value of wavelength.
  • This phenomenon of chromatic dispersion essentially consists of a widening of the duration of the pulses forming the signal during transit through the fibre, this widening being due to the fact that the different chromatic components of each pulse, each characterized by its own wavelength, travel at different velocities in the fibre.
  • pulses which follow each other in time and are quite distinct from each other at the moment of transmission can become partially superimposed on reception, after travelling along the fibre, up to the point where they are no longer distinguishable as separate entities, causing an error in reception.
  • Chromatic dispersion can be reduced by using, in place of the ordinary SI (step index) fibres, which have a zero dispersion at a wavelength in the region of 1300 nm, transmission fibres in which the chromatic dispersion cancellation point is shifted, these being known as DS (dispersion shifted); the optical characteristics of these fibres are designed in such a way that the chromatic dispersion cancellation point is brought to a wavelength in the region between 1500 and 1600 nm, which is commonly used for telecommunications.
  • SI step index
  • Fibres of this kind are defined in ITU-T Recommendation G.653 of March 1993, which specifies that the chromatic dispersion of the fibre should be cancelled nominally at a wavelength ⁇ 0 of 1550 nm, with a tolerance of 50 nm with respect to this value.
  • In-fibre Bragg gratings are formed by an alternation of areas having a high refractive index with areas having a low refractive index. The distance between these areas is called the pitch of the grating. The pitch of the grating determines which wavelengths are reflected and which are transmitted.
  • Patent application WO9636895 describes a method for writing this type of grating in an optical fibre. To compensate the chromatic dispersion, a proposal was made in an article by F. Ouellette, published in Optics Letters, vol. 12, No. 10, pp. 847-849, October 1987, and in US Patent 4,953,939, in the name of Epworth, of 04/03/90, to use an optical fibre with distributed Bragg reflection with a variable-pitch grating (chirped grating).
  • Patent application WO9726581 describes a Bragg grating fitted on a dimorphous element. In response to an electrical control signal, this dimorphous element bends in such a way as to modify the spectral response of the Bragg grating.
  • Such a Bragg grating fitted on such a dimorphous element is used as a chromatic dispersion compensator.
  • the torsion of the dimorphous element causes a modification of the pitch of the grating of the linear type; in other words, as the dimorphous element is bent, the pitch at any point of the grating is modified by the same amount.
  • a plurality of mutually independent transmission signals have to be sent along the same line, consisting of optical fibres, by means of multiplexing in the optical wavelength domain;
  • the transmitted signals can be either digital or analog, and are distinguished from each other in that each of them has a specific wavelength, separate -from that of the other signals.
  • channels specific wavelengths of predetermined amplitude, termed "channels" in the following text, have to be assigned to each of the signals at different wavelengths.
  • These channels each identified in the following text by a wavelength value, called the central channel wavelength, have a certain spectral amplitude around the central wavelength value, which depends, in particular, on the characteristics of the signal source laser and on the modulation imparted to this to associate a data element with the signal.
  • Typical values of spectral amplitude of the signal emitted by a laser, in the absence of modulation, are in the region of 10 MHz; in the presence of external modulation, at 2.5 Gbit/s for example, the spectral amplitude is approximately 5 GHz.
  • the wavelength separation between the channels is conveniently of the order of nanometres or fractions of nanometres.
  • the applicant has tackled the problem of compensating the effects of chromatic dispersion in multiple-wavelength telecommunications systems, in other words in systems in which signals at different wavelengths are transmitted simultaneously along the line (WDM).
  • WDM line
  • the chromatic dispersion is different for each channel, and therefore, in order to compensate the effects of this phenomenon accurately, it is advantageous to use a dispersion compensator for each channel of the multiple-wavelength signal after the WDM signal has been demultiplexed.
  • the applicant has considered the problem of making a component capable of compensating the chromatic dispersion in a multiple-wavelength system.
  • the applicant has found that it is possible to compensate the chromatic dispersion of each channel of a multiple-wavelength signal by forming a variable-pitch Bragg grating and modifying the said variable pitch appropriately according to the channel, by means of a distributed elongation of the said grating.
  • the applicant has found that, by fixing the said grating, made in an optical fibre for example, to a supporting substrate, which undergoes a non-linear elongation effect, it is possible to compensate the effects of chromatic dispersion on a channel of the said WDM signal.
  • the form of the said substrate is such that it undergoes a non-linear elongation, with a consequent equivalent elongation of the grating.
  • an elongation is predetermined, and is dependent on the central wavelength of the channel.
  • the present invention relates to an optical device for compensating chromatic dispersion, comprising a variable-pitch Bragg grating having a predetermined reflection wavelength and a predetermined chirping factor, and a substrate, on which this grating is integrally mounted, and which can be elongated in such a way as to cause a change in the said predetermined chirping factor.
  • the said grating is fitted into a longitudinal central groove of the said substrate.
  • the said substrate comprises a central portion essentially of truncated conical shape, having the inclined sides curved according to a predetermined profile of curvature.
  • the said profile of curvature is a hyperbolic profile.
  • the said Bragg grating is formed in an optical fibre.
  • the said optical device additionally comprises a traction device for elongating the said substrate.
  • the said substrate comprises a first portion and a second portion in which are formed holes which can interact with the said traction device for elongating the said substrate.
  • Figure 1 shows a Bragg grating 3.
  • ⁇ is the chirping factor which can compensate the effects of the dispersion at a given wavelength ⁇
  • ⁇ is the chirping factor which can compensate the effects of the dispersion at a given wavelength ⁇
  • the applicant has found that it is possible, for example, to modify the chirping factor in this way by elongating the grating in a differentiated way.
  • the areas with a high refractive index must be moved away from each other in a progressive way.
  • Figures 2a to 2c show a device for compensating the effects of chromatic dispersion according to the present invention, comprising a substrate 2 which is preferably made in a material having sufficient elasticity to withstand an elongation of approximately 1/10 of its length.
  • suitable materials for the substrate are metals, for example aluminium.
  • the said substrate is preferably of elongate shape overall, comprising a first portion 21, preferably of rectangular shape, and a second portion 23, also preferably of rectangular shape. Between the said first and the said second portion, the substrate comprises a central portion 22, essentially of truncated conical shape, having its inclined sides 221 and 222 curved according to a predetermined profile of curvature.
  • the said profile is preferably a hyperbolic profile.
  • This central portion has its two rectilinear sides connected to the said first portion and to the said second portion of the substrate.
  • the substrate also comprises a longitudinal groove 24, located in a central position and preferably passing through all three portions of the substrate.
  • a variable-pitch Bragg grating (not shown in Figure 2) is positioned in the said central groove. Preferably, the whole length of this grating is fixed within the groove, in such a way that both the substrate and the component undergo the same elongation.
  • a pair of holes 211 and 212 is formed in the said first portion 21, and a pair of additional holes 231 and 232 is formed in the said second portion 23, these holes being used for fixing the substrate to means for elongating the said substrate.
  • These means can equally well be manual elongation means, for example a lever or a knob, or automatic elongation means, for example a miniature electric motor.
  • Figures 3a and 3b show the substrate of Figures 2a-2c, in which a Bragg grating 3 is located within the longitudinal groove.
  • This grating is mounted integrally within the groove, by means of an epoxy adhesive for example; in general, the component can be fixed within the groove in any equivalent way in order to make the grating integral with the substrate and not to prevent the elongation of both the substrate and the grating.
  • An example of an adhesive of this type is an epoxy resin, Epo-Tek H72, made by Epoxy Technology, Inc.
  • Figure 4 shows schematically a substrate 2 with a grating 3 fitted into it, in a first state of elongation, on which has been superimposed the same substrate elongated through a predetermined length (indicated by A in Figure 4).
  • the areas of high reflection of the grating fitted into this support are shown by vertical lines, which for ease of reference have been extended over the whole width of the support. The figure shows that the areas of high reflection move away from each other progressively in a non-linear way.
  • the grating in the first state of elongation is shown with a fixed pitch. Following the elongation, the grating becomes a chirped grating. In fact, a chirped grating which is elongated according to the method of the present invention increases its chirping factor.
  • the grid of wavelengths used by the transmitted channels is preferably 25-50 GHz, for transmission speeds of 10-40 Gbit/s (grid according to ITU-T recommendations).
  • a grating having a length of approximately 3 cm, with an initial chirping factor of 4.76 x 10 -9 and a Bragg wavelength centred on the wavelength of the channel with the lowest wavelength (1530 nm).
  • the elongation of the substrate and of the grating must be such that the chirping factor is raised to 1.1 x 10 -8 to compensate the dispersion of the channel with the longest wavelength.
  • the device for compensating chromatic dispersion according to the present invention is advantageously applicable to multiple-wavelength telecommunications system in which, at the end of the line, the multiple-wavelength signal is broken down by a demultiplexer into its individual components, and in which each component (channel) is compensated individually.
  • the device according to the present invention permits an adjustment of the chirping factor in such a way that it can be applied to any channel.
  • the device according to the present invention can be produced easily in the initial (non-elongated) state in a plurality of individual devices. Each individual device can subsequently be adjusted to the channel wavelength of the system which is to be compensated. This reduces the production costs of the device, since all the individual devices for a single telecommunications system can be serially produced.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Communication System (AREA)
EP01830435A 2001-06-28 2001-06-28 Optische Einrichtung zur Kompensation der chromatischen Dispersion Withdrawn EP1271199A1 (de)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP01830435A EP1271199A1 (de) 2001-06-28 2001-06-28 Optische Einrichtung zur Kompensation der chromatischen Dispersion
US10/184,711 US6760519B2 (en) 2001-06-28 2002-06-27 Optical device for compensating chromatic dispersion

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP01830435A EP1271199A1 (de) 2001-06-28 2001-06-28 Optische Einrichtung zur Kompensation der chromatischen Dispersion

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2868632A1 (fr) * 2004-04-06 2005-10-07 Alcatel Sa Module optique de compensation de dispersion chromatique

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0867736A2 (de) * 1997-03-26 1998-09-30 Jds Fitel Inc. Verfahren und Vorrichtung zur Abstimmung der Wellenlänge und der Bandbreite eines optischen Gitters
EP0989438A1 (de) * 1998-09-24 2000-03-29 Lucent Technologies Inc. Abstimmbares optisches Fasergitter mit verteilter Rückkopplung
EP1024391A1 (de) * 1999-01-26 2000-08-02 Lucent Technologies Inc. Verfahren zur Herstellung von optischen gechirpten Gitter mit einem intrinsisch gechirpten Gitter und externem Gradienten
EP1024376A1 (de) * 1999-01-26 2000-08-02 Lucent Technologies Inc. Optische Gittervorrichtung mit variabler Beschichtung

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0867736A2 (de) * 1997-03-26 1998-09-30 Jds Fitel Inc. Verfahren und Vorrichtung zur Abstimmung der Wellenlänge und der Bandbreite eines optischen Gitters
EP0989438A1 (de) * 1998-09-24 2000-03-29 Lucent Technologies Inc. Abstimmbares optisches Fasergitter mit verteilter Rückkopplung
EP1024391A1 (de) * 1999-01-26 2000-08-02 Lucent Technologies Inc. Verfahren zur Herstellung von optischen gechirpten Gitter mit einem intrinsisch gechirpten Gitter und externem Gradienten
EP1024376A1 (de) * 1999-01-26 2000-08-02 Lucent Technologies Inc. Optische Gittervorrichtung mit variabler Beschichtung

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2868632A1 (fr) * 2004-04-06 2005-10-07 Alcatel Sa Module optique de compensation de dispersion chromatique
EP1585238A1 (de) * 2004-04-06 2005-10-12 Alcatel Optisches Modul zur Kompensation der chromatischen Dispersion
US7177501B2 (en) 2004-04-06 2007-02-13 Alcatel Optical chromatic dispersion compensation module

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